The present invention relates to a magnetic bubble memory device having a major-minor loop structure, and more particularly to a device of the above-mentioned type which provide a means for storing information regarding of defective minor loops.
As a prior art method for solving the problem of defective minor loops in a magnetic bubble memory device having a major-minor loop structure, the following method has been proposed. That is, some loops are chosen as the reserve minor loops from a plurality of minor loops, the address information of the defective minor loops is stored in an external semiconductor fixed memory device, i.e. ROM (See "Electronics" Aug. 4, 1977, Page 85). When an access for writing information into a defective minor loop or an access for reading information from a defective minor loop occurs, a reserve minor loop receives an access after an address conversion is effected by means of the external semiconductor fixed memory device. This prior art method, however, is disadvantageous in that the entire magnetic bubble device becomes large in size and complicated in structure, because of the existence of the external semiconductor fixed memory device.
Another prior art method for solving the above mentioned problem has been proposed in which a special minor loop for storing the information regarding defective minor loops and a special bubble transfer gate solely for said special minor loop are used, and an access to the information regarding defective minor loops is effected through said special bubble transfer gate (See "Electronics", Aug. 17, 1978, Pages 39 and 40). This prior art method, however, is also disadvantageous in that, since it is necessary to provide the special bubble transfer gate solely for said special minor loop, and said special bubble transfer gate requires an installation of a conductor and a terminal for said special bubble transfer gate, the structure of the magnetic bubble memory device becomes complicated.
The present invention has been invented to avoid the above described disadvantages in the prior art devices and to introduce a novel structure of a magnetic bubble memory device having means for dealing with the problems of writing information into and reading information from a defective minor loop.